1. Field of the Invention
The present invention relates to a display device, and more particularly, it relates to a light emitting display using electroluminescence of organic materials.
2. Description of the Related Art
In general, an organic light emitting diode (referred to as “OLED” hereinafter) display is a display device that electrically excites phosphorus organic components, and represents an image by voltage-programming or current-programming M×N numbers of organic light emitting pixels.
The organic light emitting pixels can also be referred to as organic light emitting diodes (hereinafter referred to as OLEDs), as they have characteristics similar to a diode. FIG. 1 schematically depicts a structure of an OLED. The OLED includes anode (e.g., indium tin oxide: ITO), organic thin film, and cathode (e.g., metal) layers. The organic thin film layer has a multi-layered structure including an emission layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) so as to balance electrons and holes and to thereby enhance efficiency of light emission. Further, the organic thin film separately includes an electron injection layer (EIL) and a hole injection layer (HIL). Several light emitting pixels (OLEDs) are arranged in a matrix format forming an organic electroluminescence display panel.
Methods of driving the organic light emitting pixels having the foregoing configuration include a passive matrix method and an active matrix method. The active matrix method employs a thin film transistor (TFT). In the passive matrix method, an anode and a cathode are formed crossing each other, and a line is selected to drive the organic light emitting pixels. In the active matrix method, a pixel electrode of indium tin oxide (ITO) is coupled to the TFT and a voltage maintained by capacitance of a capacitor coupled to a gate of the TFT drives the light emitting pixel. The active matrix method hence has a rather complicated pixel circuit but the pixel circuit of this driving method emits light longer and consumes less current, thereby enhancing display quality.
Also, the lifespan of the OLED is determined by the amount of current flowing thereto, and thus the lifespan of the OLED is reduced as the amount (or total amount) of current flowing to the OLED is increased. Accordingly, a method for improving display quality while reducing the amount (or total amount) of current flowing to the OLED is desired.